1. Field of the Invention
The present invention relates to a controller for a direct-injection internal combustion engine that is installed in a vehicle or the like and a method of controlling the direct-injection internal combustion engine. More specifically, the present invention relates to a controller for a direct-injection internal combustion engine and a method of controlling the direct-injection internal combustion engine that perform fuel injection control for maintaining good operational condition after initial combustion at the time of engine startup under very low temperature conditions.
2. Description of the Related Art
In a direct-injection internal combustion engine (hereinafter also referred to as the direct-injection engine), a fuel injection valve (injector) is provided for each cylinder. The fuel, such as gasoline, is directly injected into combustion chambers via the fuel injection valves, and mixed with intake air introduced from inlet ports into the combustion chambers to form a mixture, which is ignited by ignition plugs. The direct-injection engine is excellent because of low fuel consumption, low emission and high power output. For this reason, the demand for the engine is rapidly increasing.
However, in the direct-injection engine, the time period from when the fuel is injected to when the fuel reaches the ignition point is short as compared to that of a port-injection engine that injects the fuel into the inlet port. For this reason, when the engine is started at a very low temperature (below −25° C., for example), vaporization of the fuel injected into the cylinders becomes insufficient. As a result, fine ignition cannot be achieved, and the startability becomes worse.
As measures against such a problem that arises when the engine is started under very low temperature conditions, there are a method in which, when the engine is cranked at the time of engine startup under very low temperature conditions, the ignition is stopped (the ignition is cut off) for at least one cycle (see Japanese Patent Application Publication No. JP-A-2000-97071, for example), and a method in which only fuel injection is performed while cutting off the ignition of the ignition plugs for a predetermined period of time at an early stage of the engine startup (ignition cut-off period), and ignition is started while performing the fuel injection after the injection cut-off period has elapsed (see Japanese Patent Application Publication No. JP-A-11-270387, for example). By cutting off the ignition in this way, it becomes possible to accumulate the fuel, which will contribute to the ignition, in the cylinders, whereby it is possible to ensure the ignition (to achieve favorable initial combustion).
However, in direct-injection engines, even if favorable initial combustion is achieved by virtue of the ignition cutting-off control described above or the like at the time of the engine startup under very low temperature conditions, the operational condition can become worse due to the fuel injection period set after the initial-combustion stage. In particular, in direct-injection engines for which great importance is attached to the performance, in which, for this reason, the operation angle of the intake cam is set to a large angle, and in which combustion is weak in a startup state, or in direct-injection engines in which friction is large, if the fuel injection period set after the initial-combustion stage is a period during which wetting of the injection plugs is prone to occur, smoldering of the injection plugs occurs at an early stage or the middle stage of the engine startup, which can make it impossible to start the engine.
As technologies for controlling the fuel injection period while the engine has not yet reached a state where complete combustion is achieved (a state where the engine can operate in a self-sustaining manner) at the time of engine startup, there are methods described in Japanese Patent Application Publication No. JP-A-2003-269222 and Japanese Patent Application Publication No. JP-A-09-242586 described below, for example.
In a method described in Japanese Patent Application Publication No. JP-A-2003-269222, it is determined whether the engine is operating in a startup state where complete combustion is not achieved yet. If it is determined that the engine is operating in a startup state where complete combustion is not achieved yet, until complete combustion is achieved, the injection start timing is retarded relative to the normal injection start timing that is adopted after complete combustion has been achieved. In the method described in Japanese Patent Application Publication No. JP-A-09-242586, the fuel-injection start time is set so that, at the time of engine startup (before complete combustion is achieved), fuel injection is completed in good time before a compression stroke ends.
The method described in Japanese Patent Application Publication No. JP-A-2003-269222 is a method for solving a problem that, when a port-injection engine is operating in a startup state where complete combustion is not achieved yet, fuel shortage due to port wetting (the adhesion of fuel to the inner wall surface of the port) occurs. Specifically, this is a method in which, in a startup state, until complete combustion is achieved, the injection start timing is retarded relative to the normal injection start timing that is adopted after complete combustion has been achieved, so that the injection amount at the time of engine startup is increased by a certain amount. The problem that smoldering of the ignition plugs occurs after the initial combustion at the time of the engine startup under very low temperature conditions cannot be solved by applying the method described in Japanese Patent Application Publication No. JP-A-2003-269222 to the direct-injection engine.
The method described in Japanese Patent Application Publication No. JP-A-09-242586 is a method used to prevent the actual injection end time point from being significantly retarded relative to a predetermined injection end time point when the number of cranking revolutions is rapidly increased during engine startup (before the complete combustion is achieved). The problem that smoldering of the ignition plugs occurs after the initial combustion at the time of the engine startup under very low temperature conditions cannot be solved by using the method described in Japanese Patent Application Publication No. JP-A-09-242586.